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SOIL & WATER MANAGEMENT & CONSERVATION

Estimating Plant-Available Water Capacity for Claypan Landscapes Using Apparent Electrical Conductivity

^a Dep. of Environmental Sciences, 2323 Geology Bldg., Univ. of California, Riverside, CA 92521
^b 302 ABNR Bldg., Dep. of Soil Environmental and Atmospheric Sciences, Univ. of Missouri, Columbia, MO 65211
^c 269 Agricultural Engineering Bldg., USDA-ARS, Cropping Systems and Water Quality Research Unit, Columbia, MO 65211

^* Corresponding author (pingping.jiang{at}ucr.edu).

Information on plant-available water (PAW) capacity (PAW_c) variation within a field is useful for site-specific management. For claypan soils, established relationships between soil apparent electrical conductivity (EC_a) and topsoil thickness suggested the hypothesis that profile PAW_c could be estimated by assuming a two-layer soil composition, a silt loam topsoil layer and a silty clay sublayer, with known PAW fraction values for each layer. Objectives were (i) to investigate the direct relationships between EC_a and the upper and lower limits of PAW_c, and (ii) to test the previously stated hypothesis. Nineteen and 18 soil profile samples were taken from two Missouri claypan fields in October 2005. The lower limit of PAW_c was determined at –1500 kPa soil water pressure. Samples were taken again from the same locations in March 2006 to determine the upper limit of PAW_c. Calculations were on a 1.2-m basis. The direct relationship between EC_a^–1 and profile PAW (PAW_1.2) was significant, with regression r² values of 0.67 and 0.87 and RMSEs of 30 and 20 mm for Fields 1 and 2, respectively. The RMSEs for two-layer-estimated PAW_1.2 were 14 and 16 mm for Fields 1 and 2, respectively, or 7.6 and 8.6% of the respective mean measured PAW_1.2. With the two-layer approach, some underestimates of PAW_1.2 resulted from underestimation of topsoil thickness, whereas overestimates were attributed to soil horizons being short of field capacity at sampling due to slow recharge. The resulting field-scale PAW_c information is useful in site-specific decision making for soil and water management.

Abbreviations: C, clay • EC_a, bulk soil apparent electrical conductivity • LL_1.2, lower limit of plant-available water for a 1.2-m soil profile • PAW, plant-available water • PAW_c, plant-available water capacity • PAW_1.2, plant-available water for a 1.2-m soil profile • SIC, silty clay • SICL, silty clay loam • SIL, silt loam • UL_1.2, upper limit of plant-available water for a 1.2-m soil profile

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				P. Jiang, N. R. Kitchen, S. H. Anderson, E. J. Sadler, and K. A. Sudduth Estimating Plant-Available Water Using the Simple Inverse Yield Model for Claypan Landscapes Agron. J., May 7, 2008; 100(3): 830 - 836. [Abstract] [Full Text] [PDF]